CYLD is a tumour suppressor gene involved in regulation of several proliferation-associated pathways, including NF-κB, Wnt, Notch and TGF-β, potentially suggesting that metastatic tumour heterogeneity driven by further adaptation to increased proliferative phenotypes does occur, though less ubiquitous than the heterogeneity observed in primary tumours. The gene discussed is CYLD; the disease is neoplasm.